CORVALLIS, Ore. – A team of Oregon State University researchers will use a $620,000 grant from the U.S. Environmental Protection Agency to study the impacts of large sediment deposits on coastal estuaries during winter flood events and to document the recovery of the benthic communities.

The sediment discharge in Northwest rivers appears to be increasing, scientists say, because of an increasing number of intense precipitation events; changes in the landscape through logging, agriculture and development; the evolution of complex river systems into channels; and the drainage of tidal marshes through diking and other human influences that reduce the buffering capacity of natural systems to absorb sediment load.

The OSU researchers will study the impact of increasing sediment loads on worms, clams and small crustaceans – estuarine species that represent important prey for Dungeness crab, fish and seabirds, according to Anthony D’Andrea, an assistant professor in the OSU College of Oceanic and Atmospheric Sciences and a co-principal investigator on the study.

“This is the first step in assessing the risks to estuaries posed by extreme rain events in the region,” D’Andrea said. “Muddy, rain-swollen rivers are a signature characteristic of the Pacific Northwest, yet the impact of flood sedimentation events on benthic communities is poorly understood.”

The OSU researchers also will track the response of native and non-indigenous species to sedimentation events to see if this type of disturbance allows non-native species to gain a foothold and thrive at the expense of native species.

D’Andrea and co-principal investigator Rob Wheatcroft will stage their experiment at Netarts Bay near Tillamook because it has no river system and the organisms in the tidal flats have not previously been exposed to constant flooding.

“Studying benthic communities in established flood plains is tricky,” D’Andrea pointed out, “because the resident organisms may already be adapted to flood events and have a quicker recovery. Starting from scratch will give us better baseline data and lead to a more accurate predictive model.”

The researchers will add a layer of fine sediment from local watersheds onto study plots in Netarts Bay in December and compare them with nearby control plots. A subset of those plots will be subjected to a second simulated sedimentation event 40 or 50 days later to see if multiple events have different impacts. December and January are peak rainfall months for Tillamook County, which has seen increasing precipitation problems in recent years.

Between 1910 and 1950, the Wilson River entering Tillamook Bay experienced three total peak runoff events. Since 1960, the Wilson has seen 17 peak events, including six in the 1990s alone. Damage from these floods during a six-year period alone topped $60 million.

Likewise, major sedimentation events have been increasing in Pacific estuaries and sediment deposits of up to 12 centimeters thick have been documented.

This is one of the first major experiments looking at major sedimentation impacts on Northwest estuaries. A pioneering study in New Zealand found that many species die due to initial smothering because of sediment deposition and recovery can take many months, even years.

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Anthony D’Andrea,